In the sense of the invention, miniature drives or microdrives are electrical drives having a continuous output of at most 1000 W.
Transmissions for electrical miniature drives or microdrives in particular lead to a multiplication of the torque generated by the motor at the transmission output with the simultaneous reduction of the output rotational speed by a reduction ratio. Due to losses from friction, the influence of the reduction ratio as well as the transmission self-locking effect resulting therefrom, the torques acting at the output are not always transmitted to the motor in proportion to the reduction. Conclusions as to the torque generated at the transmission output can thus not always be directly arrived at by means of a measurement of the motor torque. In order to, nevertheless, determine it, the output torque can be measured.
Torques can be measured, for example, by determining the resulting deformation of elastic regions of the flexible element. In this case, the measurement of the deformation directly at the moved driven shaft is very complex, particularly in precision dimensions due to the narrow spatial conditions. A measurement of the reaction torque circumvents the need to transmit information to and from moved parts. Strain gauges are very often used for the measurement of forces, torques, and the deformations resulting therefrom.
For example, a torque measuring member having strain gauges for a planetary transmission device is known from DE 10 2006 057 539 A1. Due to the very small changes in the electrical properties, special evaluation electronics having measurement amplifiers are necessary, which as a rule require the signals from a plurality of strain gauges. The strain gauges must be firmly applied to the deforming element and electrically contacted. In addition to the installation complexity, the accessibility, in particular for mounting the sensors, is problematic under narrow spatial conditions.
The object of the invention is to provide a transmission having a torque measuring member for measuring the torque at the driven shaft, which torque measuring member is configured particularly small and compact, is simple and cost-effective to manufacture and to install, and can be used in a flexible manner.
The object is inventively achieved by the features of the invention described herein. Since a magnetic encoder system is disposed on the flexible element, which magnetic encoder system has a magnetic field generating element and a magnetic field measuring element for measuring a rotatory deflection of the flexible element, wherein the flexible element is disposed axially between the transmission mechanism and the attachment flange, a particularly compact design is made possible. In particular, the use of a magnetic encoder system allows a precise registration of the torque at little expense and simpler installation.
In an advantageous embodiment of the invention, the flexible element circumferentially encloses the driven shaft, wherein it transforms a torque generated at the driven shaft into a rotatory deflection of the flexible element. In particular, the flexible element includes at least three struts extending axially parallel to the driven shaft. In this case, it is particularly advantageous if the flexible element, in particular its struts, has a radial height that is at least twice as large as the tangential thickness of the flexible element, in particular of its struts. The flexible element, in particular its struts, advantageously has an axial length that is at least four times as large as the tangential thickness of the flexible element, in particular of its struts. As a result of such a design, a high rigidity, thus insensitivity with respect to radial disruptive forces, and a low rigidity, thus high sensitivity to rotational torques is achieved.
In one embodiment of the present invention, the torque measuring member, the attachment flange, and the driven bearing flange form a modular functional subassembly, which can be assembled independently of a transmission housing with the transmission mechanism and the driven shaft and is configured as an assembled part that can be placed on the driven shaft. The flexible element and the attachment flange are preferentially configured in one piece. In particular, the driven bearing flange includes at least two driven bearings, wherein one or two driven bearings are disposed axially inside the flexible element. This further reduces the installation space and simplifies the assembly of the transmission.
In a further advantageous embodiment, the magnetic encoder system is disposed in the intermediate space of the struts of the flexible element. In particular, the magnetic encoder system is disposed on the flexible element such that in the event of a rotatory deflection of the flexible element, the magnetic field generating element is displaced tangentially with respect to the magnetic field measuring element.
In particular, the magnetic field generating element is advantageously disposed radially, axially, or tangentially spaced on the flexible element, wherein the magnetic field generating element is disposed on a first partial element of the flexible element, which first partial element is connected to a first axial extremity of the flexible element, and the magnetic field measuring element is disposed on a second partial element of the flexible element, which second partial element is connected to an opposing second axial extremity of the flexible element.
Furthermore it is advantageous, if a mechanical overload protection is disposed between the struts of the flexible element. In this case, the overload protection is configured in particular as a mechanical stop, wherein the stop acts between the one and the other axial side of the flexible element and thus acts against too far a rotation in the event of large drive torques.